Again - he wouldn't have known that the guy was using his middle name as his first from conversation. It has to be conversation + something. And the something will probably be forever unknown, because it was such a randomly fantastic hit.
At any rate, to quell any hidden mic theories - I went to the show twice and felt around under every single table I could get my hands on. I also had an accomplice sit outside with one of those scanner thingies like cops use to determine if info was being sent that way. It was not.
I think you are over thinking this, RemieV. John Edward didn't need anything more than what he already had and some quick thinking. The truth is, I think this isn't even that amazing a trick, once I realized just how simple it really was. Which makes it an excellent example of how mentalists work, and how sometimes even not-that-great mentalist tricks can occasionally fool seasoned experts like yourself, as Garette was saying earlier.
Here's the setup. JE, or one of his assistants, heard Liam introduce himself either to you or to his tablemates. I believe you that you don't think there were any mics in the room. Maybe there weren't. The bottom line here though is that the only thing JE had to know to pull off the trick is something that Liam himself said at least twice either in the theater or waiting in line to get into the theater. And actually, JE didn't even need to hear it all that well. Maybe he heard it as "Lee" or "Lynn" or something like that. All he had to know is that it was an "L" sounding name. He stowed that information away, planning to use it at some point in the show.
For whatever random reason, JE comes up with the name Joshua, and aims it toward Liam's table. Maybe he was intending to work one of Liam's tablemates, and then work Liam's "L" name in later on. Who knows. It doesn't matter. The only thing that matters is that he says the name Joshua and Liam reacts. You said Liam stood up. I am sure that Liam probably reacted in such a way as to make it clear that he was the Joshua. Maybe he stood up really fast. Maybe he reacted like I said before, with surprise and a hand gesture that said "Oh wow, that's me!"
So now JE has something. He KNOWS that Liam has called himself another name. So he rolled with it and pretended he was getting something "weird".
"So, this is weird. I am getting that YOU are Joshua"
Well, duh. Joshua just stood up and was obvious.
"Yes"
HIT says the audience mentally.
"But you introduced yourself by another name.."
"Yes"
HIT two! says the audience mentally
"Hand the microphone to someone else.. What name did this man introduce himself as?"
"Liam"
HIT three! says the audience mentally, even though we're still really on number two. This is also an excellent distraction for the audience so they don't think too hard about how JE might know how Liam introduced himself.
Then, as I said before, JE, having a good understanding of names and common nicknames, etc, quickly deducts that Liam is going by his middle name, so he pulls a little showman stunt to make this seem more amazing than it really is.
"Please take out your drivers license and show it to the people at your table"
"Joshua Liam Smith" someone reads out.
HOLY SMOKES!!! says the audience mentally, and so does RemieV, because it FEELS like John Edward just knew this guys full name.
And I'm willing to bet that if you asked several true believers what they remember about that incident, at least a few of them would say that they distinctly remember John Edward KNEW this guy's full name, AND that the guy went by his middle name. AMAZING! What are the odds of that???!!
The truth is though, obviously, that he didn't know any such thing. John Edward only knew that Liam did not introduce himself as Joshua.